Patent Documents 1 and 2 disclose a manufacturing method of a vehicle wheel disk manufactured from a disk material of a flat plate, for a single-mounted type wheel (including a disk having a hat and used for a passenger car, etc.)
Patent Documents 1 and 2 disclose a manufacturing method of a vehicle wheel disk where a disk flange is reduced in thickness by ironing the disk flange.
However, there are the following problems with the conventional manufacturing method of a vehicle wheel disk:
In the manufacturing method disclosed in Patent Documents 1 and 2, only the disk flange is reduced in thickness by ironing. The disk flange is substantially constant in diameter, extends parallel to an axis of the disk, and is limited in length. Thus, lightening the disk is insufficient.